The present invention relates to utility wheels and, in particular, to a plastic, blow molded, compositional wheel.
Within recent times and for many applications, plastic wheels have replaced traditional pneumatic or rubber covered wheels. For limited use or lightweight applications, such as with barbecue carts, lawn mowers, trash containers and many other devices, plastic wheels can serve the same purpose, but at relatively lower costs. Commonly encountered plastic wheel constructions are formed by blow molding, rotational molding or injection molding. Examples of some blow molded wheels can be seen at U.S. Pat. Nos. Des. 221,424 and Des. 325,011, the latter patent being assigned to the present assignee. Such wheels provide a homogeneous, hollow wheel construction which exhibits a relatively hard tread surface.
Injection molded wheels can either comprise a semi-pneumatic construction or a solid construction. A semi-pneumatic wheel typically provides an injection molded, solid rim in a comparable configuration to conventional metal rims and to which an appropriate rubber or elastomer tire is mounted. Alternatively, the rim can be constructed to accept a solid rubberized cap or tread piece. Such a tread piece commonly mates with cooperating projections or flanges at the rim to mechanically retain one to the other. A wheel of the latter construction type is shown at U.S. Pat. No. 3,604,756.
Each type of wheel has certain advantages and disadvantages. Injection molded wheels accommodate conventional tires and possibly heavier duty use, but necessarily require very costly molds. Molding characteristics also limit the rim size.
In contrast, blow molded (i.e. extrusion blow molded) and rotational molded wheels require less costly molds. Blow molded wheels can also be cost effectively produced in a variety of design configurations offering structural strengths exceeding injection molded wheels.
Inherent negatives of such wheels, however, are that the core of the wheels are hollow and thus the wheels tend to be "noisy". Depending upon the wheel design, the wall thickness of the wheel may also not be uniform throughout the wheel and thus trade-offs must be made between structural design and material costs. Because the wheels are made entirely of plastic, they also tend to offer less traction than rubber tread wheels. Rotational molded wheels have additional inherent limitations in design flexibility over blow molded wheels.
To the extent applicant is aware of other composite wheels including plastic or elastomeric treads, U.S. Pat. Nos. 4,485,135 and 4,485,136 disclose alternative methods for patching pneumatic, elastomeric tires that mount to undisclosed rims. U.S. Pat. No. 4,530,959 discloses a pneumatic tire having a sulfur cured elastomeric tread composition. U.S. Pat. No. 2,197,127 discloses a pneumatic tire including a flexible rubber face and to which an olefin based plastic is bonded via an intermediate uncured rubber composition.
U.S. Pat. No. 4,490,197 also discloses a conventional method for retreading a rubber pneumatic tire which comprises the abrading and buffing of the surface of a tire carcass, prior to molding a replacement tread to the carcass.
U.S. Pat. No. 4,095,637 discloses a composite wheel including a preformed cast metal rim and to which a rubber tire tread is injection molded. The rim is separately prepared from the tread, inserted into the injection mold and the tread is cast in place about the rim. A flow melt method is not disclosed nor a wheel including a blow molded rim and relative to which a separately prepared tread surface is flow melt bonded.
Appreciating the foregoing advantages and disadvantages of blow molded wheels and the state of the art, the present invention was conceived. The invention comprises a blow-molded wheel construction that is relatively noise free. The wheel also provides a tread surface of controlled thickness and having tailorable traction properties.